1. Field of the Invention
The invention relates to a lubricant and release agent for the manufacture of tires. Mcre particularly, the present invention concerns an aqueous dispersion of a lubricant and a release oil used in conjunction with fillers having a leaf-shaped structure and dispersing agents.
2. Description of the Prior Art
In the manufacture of tires, an unvulcanized carcass shell is placed in a metal mold. By blowing up a rubber bag in the interior of the green carcass shell, the tire is pressed against the mold and vulcanized by the action of heat. While being blown up, the expandable rubber bag must slide over the tire carcass. After the vulcanization of the rubber mixture, the rubber bag must be separated from the tire. For this purpose an oily lubricant and release agent is used. This release agent is sometimes referred to as a bag or cold-pressed molding lubricant.
These lubricant and mold release agents generally consist of a silicone oil, a polyalkylene glycol, mica, as a filler, with a leaf-shaped structure and dispersing agents. They may exist in the form of an aqueous or a solvent-containing preparation. Such preparations are described, for example, in German Offenlegungsschrift No. 19 49 618. According to this German Offenlegungsschrift, a mixture is used which consists of
1. 2 to 10 weight percent of liquid dimethylpolysiloxanes with a viscosity of at least 30,000 cSt at 25.degree. C.; PA0 2. 5 to 20 weight percent of ethylene or propylene glycols or copolymers of these compounds with a molecular weight of at least 1000; PA0 3. 25 to 50 weight percent of mica with a particle size of 160 to 600 mesh; PA0 4. 0.5 to 5 weight percent of bentonite clay and a higher polar solvent in an amount which is sufficient for the formation of a gel structure and for the thickening of the mixture; PA0 5. 0.25 to 5 weight percent of lecithin and PA0 6. 25 to 55 weight percent of a hydrocarbon solvent with a boiling point below 200.degree. C. PA0 (A) 3 to 40 weight percent of a mixture of PA0 (B) 3 to 40 weight percent of a copolymer of an alkylmethylsiloxane and a polyalkylene oxide whose alkylene oxide units consist of ethylene oxide, propylene oxide or of combinations of these, the copolymer (B) having a viscosity of at least 10,000 cSt at 25.degree. C. and containing 5 to 50 weight percent of the alkylmethylsiloxane; PA0 (C) 25 to 50 weight percent of mica with a particle size corresponding to sieves with clear mesh widths of about 0.091 to 0.021 mm; PA0 (D) 0.25 to 5 weight percent of a finely particulate magnesium silicate; PA0 (E) 0.1 to 5 weight percent of lecithin; and PA0 (F) 15 to 55 weight percent of water. PA0 (a) be water insoluble, PA0 (b) be liquid, and PA0 (c) have a viscosity of at least 8,000 mPa.times.sec.
German Auslegeschrift No. 21 25 948 discloses an aqueous siloxane lubricant for molding tires, which consists of
1. 1 to 20 weight percent of an alkylmethyl siloxane liquid with a viscosity of at least 10,000 cSt at 25.degree. C., based on the weight of the lubricant, and PA1 2. 2 to 20 weight percent, based on the weight of the lubricant, of a polyalkylene glycol with a molecular weight of at least 1,000, whose alkylene oxide units consist of ethylene oxide, propylene oxide or of combinations of these, or whose alkylene oxide units are copolymerized from ethylene oxide, propylene oxide or of combinations of these with alkylmethylsiloxanes, or
Other disclosures showing the state of the art are German Pat. No. 22 25 698, German Offenlegungsschrift No. 24 27 029 and German Offenlegungsschrift No. 22 51 685.
These known compositions do achieve a lubricating and release effect. However, they are not completely satisfactory because up to 5% rejects must be expected even when these materials are used. These rejects may be attributed to the following defects. The silicone oil contained in the preparations may migrate between the overlapping sites of the unvulcanized carcass shell so that, on vulcanization, the overlapping regions do not bond or bond incompletely or defectively to each other. Defective sites, such as, crumbling, may also be observed in the region of the sealing bead of the tires. This defect may be attributed to the same cause. The anhydrous or solvent-free, mica-containing preparation partially flakes away from the inner side of the carcass shell or is transferred to the rubber bag, resulting in defective surfaces on the inner side of the tire or in damage to the rubber bag. It is therefore also a reasonable assumption that only about 250 to 300 tires can be manufactured from one rubber bag.